Rett syndrome (RTT) is an X-linked neurodevelopmental disorder caused by mutations in MECP2, encoding methyl CpG binding protein 2 (MeCP2). RTT is the only autism-spectrum disorder with a known genetic cause and MECP2 mutations or expression defects are observed in other autism-spectrum neurodevelopmental disorders. Therefore, investigations of the role of MECP2 in the developing brain have broad relevance to mental retardation and autism. Since the discovery of MECP2 mutations as the genetic cause of RTT in 1999, the understanding of MeCP2 function has evolved. Although MeCP2 was predicted to be a global transcriptional repressor of methylated genes, MeCP2 is only required during postnatal brain development, when expression is elevated. To focus future experiments precisely on the role for MeCP2 that is deficient in the pathogenesis of RTT, a new model is proposed of MeCP2 as a dynamic neuronal nuclear factor that regulates genes involved in neuronal maturation through changes in sub-nuclear localization. The proposed experiments are designed to test the hypothesis that alternative splicing and post-translational modification of MECP2/Mecp2 exon 2 regulates sub-nuclear localization and differential protein association during neuronal maturation. Aim 1 will determine differences in sub-nuclear localization and protein association between MeCP2e1 and MeCP2e2 isoforms. Aim 2 will investigate changes in nuclear protein association and sub- nuclear localization of MeCP2 target genes. Aim 3 will identify novel targets of MeCP2 by genome-wide chromatin immunoprecipitation approaches and will test the relevance of each target gene to the pathogenesis of RTT. These results are expected to be significant in understanding the molecular pathogenesis of RTT and will be instrumental in designing future therapies to treat this devastating disorder. In addition, the results are expected to impact a broader spectrum of patients with autism and mental retardation because of overlapping pathways involving MeCP2 and post-natal neuronal maturation. PUBLIC HEALTH RELEVANCE: Rett syndrome has been considered a "Rosetta stone" for deciphering the complex genetics of autism because it is the only one of the five pervasive developmental disorders with a known genetic cause. This proposal seeks to understand how the product of the Rett gene, MeCP2, operates inside the nuclei of post-natal neurons to regulate important gene regulatory events in learning and memory. These results are expected to be significant in understanding and designing future therapies for Rett syndrome, autism, and mental retardation.